Molecular dynamics and Monte Carlo simulations of beta -cyclodextrin and its per-dimethylated derivative heptakis(2,6-di-O-methyl)-beta -cyclodextrin have been carried out in water solutions at two temperatures, 25 degreesC and 70 degreesC. The structure of the hydration shells, as well as the solute-solvent and solvent-solvent correlations have been analyzed. The negative solubility coefficient of heptakis(2,6-di-O-methyl)-beta -cyclodextrin is conditioned first of all by progressive destruction of the hydration shells around its methyl groups with temperature increase, whereas for beta -cyclodextrin with positive temperature coefficient, solution is comparable at 25 degreesC and 70 degreesC.